The present invention relates to microwave circuits and more particularly to microwave phase shifters
The use of microwave systems has been increasing as more microwave components have become available. In many microwave circuits lightweight and small size are important. As a result, such circuits are often fabricated in strip transmission line form. A strip transmission line is one in which microwave signals are carried by narrow strip conductors spaced by a dielectric region from at least one substantially wider ground conductor. A microstrip circuit is a special case of a strip transmission line circuit in which the strip conductors are disposed on one major surface of a solid dielectric substrate and the wider ground conductor is disposed on the other major surface of that substrate.
One microwave circuit which is often used as a building block in the fabrication of more complicated microwave circuits is the microwave phase shifter. One of the most common types of microwave phase shifters is the switched line phase shifter in which the phase shift is changed by switching strip conductors having different line lengths into and out of the signal path. The switching is done by diodes or other active devices. Such phase shifters suffer from several disadvantages. They require substantial substrate area for their fabrication because of the need to provide a number of separate switchable lines some of which may be as long as a quarter wavelength or a half wavelength. They are lossy devices and attenuate the signal being phase shifted. They are also relatively narrow bandwidth devices because each switched line provides an exact fraction of a wavelength at only one frequency. That frequency is usually referred to as the center frequency. The actual phase angle changes with frequency. The greater the difference between the center frequency and the operating frequency, the more the actual phase shift differs from the desired phase shift. This restricts such phase shifters to relatively narrow bandwidths of about .+-.10% =about their center frequency.
There is a need for a lightweight, compact and relatively broadband phase shifter which introduces less loss or provides some gain to the signals transmitted therethrough.